Studies are continuing on isolated mammalian muscle spindles with their capsules removed. Both extracellular and intracellular recording from axons of primary endings are employed and the receptor potential responses to applied stretch are being studied in solutions of varying ionic composition. Displacement of elements within the spindle is being followed using Nomarski optics. This is also being used in conjunction with intracellular recording and stimulation to study the contractile responses of intrafusal muscle fibers. BIBLIOGRAPHIC REFERENCES: Hunt, C.C. and D. Ottoson. Initial Burst of Primary Endings of Isolated Mammalian Muscle Spindles. J. Neurophysiol. 39:324-330 (1976). Beacham, W.S., A. Konishi and C.C. Hunt. Observations on the Microcirculatory Bed in Rat Mesocecum Using Differential Interference Contrast Microscopy In Vivo and Electron Microscopy. Amer. J. Anat. 146:385-425 (1976).